Finding the cracks is easy if you wipe it with a dye. then use a dremel or similar tool to open up the cracks.
No idea how bad the cracks are so can't give any other recommendations.
You could grind off the gell coat and recover or paint, but that's a lot of work too.
covering it as suggested above would also work as a 'fix' but unless it was completely sealed down it would trap moisture under it and could lead to more problems later on
I recently had to run through and repair cracks in 48 (out of 52!) fiberglass tub/shower units in an apartment building where the installers decided to slide them 5ft off the back of the truck onto concrete putting stars in two corners each, then went ahead and installed them, they're the type that need to be installed before all the walls are up, so there was no option of pulling them. I wiped them down with red food coloring, then used a dremel with a clear plastic sleave over the end to control the depth to v the cracks. worked, wasn't fun.